1. Field of the Invention
The present invention relates to a vacuum coating apparatus for coating films on the surfaces of electronic components, lenses or the like by evaporating a film material under a vacuum.
2. Description of the Prior Art
In a vacuum coating apparatus, a material to be deposited on object surfaces is generally accommodated in a heating element called a "boat" or a crucible and is positioned so as to confront objects to be coated. The material is evaporated by means of resistance heating, high-frequency induction heating or the like. Evaporated particles are then deposited on the object surfaces to form films thereon. Conventionally, in order to form uniform films on the object surfaces, the deposition is performed by rotating the objects confronting the boat or an entire carrier for carrying the objects.
FIG. 1 depicts a conventional vacuum coating apparatus having a vacuum deposition chamber 1, a dish-like boat 10 accommodated in the vacuum deposition chamber 1, a pair of electrodes 11 connected to the boat 10, and a dome 15 in the form of a hemispherical shell disposed above the boat 0 and confronting the boat 10. The boat 10 accommodates a film material V. The electrodes 11 extend through the vacuum deposition chamber 1 and are connected to a power source via a transformer 12 disposed outside of the vacuum deposition chamber 1. A plurality of objects, for example lenses R, are arrayed and supported on the dome 15. The dome 15 is supported at its periphery by a ring gear 13, which is rotatably supported by a bearing mechanism 17 and meshes with a pinion gear 19 driven by a drive motor 16. A sheathed heater or heaters 18 are disposed above the dome 15 so as to cover it.
A through-hole is formed at the center of the dome 15 and a monitoring member M made of, for example, glass is disposed above the through-hole. A film thickness measuring device 14 is disposed outside of the vacuum deposition chamber 1 and above the monitoring member M and measures the thickness of a film deposited on the surface of the monitoring member M in order to grasp the state of films deposited on the surfaces of the lenses R.
In the vacuum coating apparatus having the above-described construction, since the dome 15 rotates along with the heated lenses R, the relative distances between the lenses R and the boat 10 and the directions and the angles of the lenses R relative to the boat 10 vary gradually during a deposition treatment. As a result, coating films of a substantially uniform thickness are formed on the lens surfaces.
The vacuum coating apparatus of the conventional construction is, however, disadvantageous in the installation and removal of the large-sized dome 15 is somewhat troublesome, thus making it difficult to automate the entire vacuum coating operation including the installation and removal of the objects onto and from the dome 15.
This vacuum coating apparatus is also disadvantageous in that replacing the monitoring member M is troublesome. Since the monitoring member M must be replaced by a new one whenever a vacuum deposition operation is completed, replacing of the monitoring member M must be replaced upon the installation and removal of the dome 15. In automating the deposition treatment, it is particularly difficult to supply and properly position a large number of monitoring members M stored at a predetermined location one-by-one because the inside of the vacuum deposition chamber 1 is under a vacuum and is at a high temperature. If a monitoring member M is mounted in advance on the dome 15 on which the lenses R are mounted, rotation of the dome 15 is accompanied by a rotation of the monitoring member M. As a result, it becomes impossible to accurately detect the thickness of a film formed on the monitoring member M from outside of the vacuum deposition chamber 1.
The conventional vacuum coating apparatus is still further disadvantageous in that it is rather difficult to lubricate the bearing mechanism 17 for rotatably supporting the ring gear 13 and the pinion gear 19 through which a driving force from the motor 16 is transmitted to the ring gear 13. More specifically, since the inside of the vacuum deposition chamber 1 is under a high vacuum and is at a high temperature of about 300.degree. C., there is no perfectly satisfactory lubricant or no complete bearing means. It is, therefore, very difficult to maintain the rotation of the dome 15 under a desired condition.